The Qehan Lake Basin is located in the north of the Otindag Sandy Land, where the fragile eco-environment is sensitive to climate change and human activity. We analyzed land cover change and the concomitant processes of ecological change based on multi-spectral scanning (MSS), thematic mapper (TM), and enhanced TM (ETM+) images. The results showed that from 1977 to 2000, the area of dune sand increased significantly by 840.2 km, while the area of high cover grassland (HCGL), medium cover grassland (MCGL), and low cover grassland (LCGL) reduced by 140.6, 207.3, and 463.3 km, respectively. Additionally, the area of wetland decreased by 112.9 km. During the period of 1977 to 2000, the land cover condition index (LCCI) reached a low of 27.7, which indicated serious eco-environmental challenges in the Qehan Lake watershed. However, the process of desertification was reversed, and vegetation cover was gradually restored after 2000. From 2000 to 2013, the area of LCGL increased by 369.2 km (13.4%), while the area of dune sand decreased by 560.1 km (29.4%). The LCCI improved to reach 29.18 in 2013, demonstrating a significant eco-environmental improvement. Although climate change, human activity, and ecological policies have together determined the scope and extent of desertification in the watershed, the most fundamental factor in the restoration of vegetation was precipitation.
The Qehan Lake Basin (QLB) and its system of lakes are located in a marginal monsoon zone and are extremely sensitive to global climate change. In this paper, using aerial photographs from different periods, in addition to MSS, TM, and ETM images, and combining these with regional topographic maps, we analyze lake area changes from 1958 to 2010 and the relation between Qehan Lake (QL) and climate variability. Our results indicate that there was a relatively high lake level in 1959, when the area and volume of the lake were 118.9 km2 and 151.9 × 106 m3, respectively, but this level was subject to a shrinking trend until 2010, when the lake area was only 28.1 km2, and the water volume was 41.1 × 106 m3. West Qehan Lake (WQL) has experienced severe water shrinkage and lake level fluctuation. In 1958, WQL was 80.2 km2 in area and 124.1 × 106 m3 in volume. However, due to a rapid decrease in precipitation and increases in both temperature and evaporation, it began to dry up in 2002. The WQL Water area decreased by 1.82 km2/a, and the lake level declined by 7 m during 1958–2002, so it became an ephemeral lake.
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